The invention relates to a multibeam laser source with a plurality of laser light sources arranged in an array.
To set images on image carriers formed with a flat or curved surface, in particular printing forms in a printing form exposer or a direct imaging printing unit of a printing machine, use is frequently made of multibeam light sources, typically multibeam laser light sources, such as semiconductor laser or diode laser arrays, in particular. Depending upon the image information to be set, each individual light source and each individual emitter is switched on or the variables that influence the light intensity for each image point to be set on the image carrier is set or prescribed, respectively, so that each individual emitter produces a projection point with a specific light intensity. As an option, provision is frequently also made of imaging or reproduction optics for projecting the light emitted by the light sources onto the image carrier, frequently by changing the propagation direction of the light and by beam shaping, respectively.
For precise and simple image-setting or imaging of the printing form by the plurality of heretoforeknown imaging methods, it is desirable that the image points of the light sources on the image carrier lie on one projection line for the one-dimensional case, preferably on a straight line, which typically, if the image carrier is a printing form and is accommodated on a so-called printing form cylinder or printing plate cylinder, is parallel to the axis of the cylinder and, for the two-dimensional case, forms an orthogonal, in particular Cartesian projection field, respectively. Furthermore, it is particularly advantageous if the spacings between adjacent image points are uniform. Due to influences or effects arising during manufacture, the spacings of the light sources from one another frequently do not meet these requirements. Possible causes therefor are position errors of individual emitters on a substrate or a change in the geometry during fastening to a holding element, for example. In addition, reproduction or imaging errors in the reproduction or imaging optics arranged downstream to project the light sources onto image points in a projection plane often lead to deviations in the spacings from desired prescriptions thereof.
While the use of micro-optical components in reproducing or imaging optics, i.e., individual optical components which, respectively, act upon a light beam originating from only one emitter or from a few emitters, in principle, permits the light path or the course of the beam to be varied, in particular in relation to another beam from another emitter or several other emitters, there exist technical reasons which hamper a practicable realization of this concept, amongst others due to the small geometric dimensions of the micro-optical components or of the lack of a permanent fixing.
Because, in general, the image carrier upon which an image is to be set is movable relative to the image-setting or imaging device with the multibeam light source, there is a further possible way of varying the position of image points to be set on the image carrier located in the projection plane, in that the time control of the individual light sources in the multibeam light source is selected to be different so that the projection points of the light sources come to lie at desired coordinate points on the image carrier. In this way, for example with a number of light sources distributed non-uniformly in the direction of the relative movement, a number of image points distributed uniformly in this direction or distributed as desired can be produced. In the non-prepublished German Patent Application No. De 101 24 215.8 known only in-house at the corporate assignee of the instant application, an image-setting or imaging device of this general type with a plurality of light sources is described, to which a time delay device is assigned, which shifts the triggering point for driving each light source as a function of the respective spacing of the light source from a subject line in such a way that image points are produced in a projection line of the subject line on a printing form.
Electronic correction of the position of the image point by time-delayed control, using the movement of the image carrier with respect to the image-setting or imaging device, is, however, possible for a number of projection points only in the sense that a one-dimensional arrangement on the surface of the image carrier is achieved; for a multibeam light source, the light sources of which are arranged in a one-dimensional array, only a (one-dimensional) curve or else a straight or sectionally straight line can be predefined or prescribed on the (two-dimensional) surface of the image carrier. Time-delayed driving or control of the light sources takes place in such a way that triggering of the light source occurs when, during the relative movement between the image-setting or imaging device and the image carrier, the assigned projection point thereof intersects the curve on the surface. Accordingly, the image point that is produced lies on the curve. In general, with the hereinaforementioned procedure, however, it is not possible, for fundamental reasons, to influence the position of the image points produced along the curve, because, in the geometric sense, this is a (one-dimensional) projection of the position of the projection points on the surface onto the curve for non-delayed driving or control of the light sources along the direction of the relative movement. What is involved, therefore, is an only one-dimensional correction of the image point position. For a multibeam laser light source with light sources arranged in a two-dimensional array, this property therefore applies correspondingly to each line in the arrangement.
As is known, the radiation characteristic of a laser light source is influenced by the geometric arrangement of the resonator. An introduction to laser structures of semiconductor lasers is given, for example, in xe2x80x9cIntegrierte Optoelektronikxe2x80x9d (Integrated Opto-electronics) by K. J. Ebeling (Springer, Heidelberg, 1992). Furthermore, particularly for gain-guided laser diodes, it is known that the active region wherein laser activity occurs is determined by the region through which current flows, i.e., that region wherein pump energy is provided.
U.S. Pat. No. 4,791,646 discloses that a gain-guided diode laser can have a spatial distribution of the pump energy in the resonator, so to say, a tailor-made pump energy distribution. This is achieved by a two-dimensional pattern of current-guiding contacts and insulating regions on one side of the laser. The location-dependent pumping within the resonator of a large-area diode laser leads to a narrow intensity distribution in the remote field.
U.S. Pat. No. 4,719,623 describes a gain-guided diode laser with a spatial pump energy distribution, which has a nonuniform pattern of current-carrying contacts and insulating regions on one side of the laser. Although the laser is described as a field with a plurality of partial lasers, what is involved is a single-beam light source, because the individual partial lasers are coupled. Due to the feature of a nonuniform pump current distribution, oscillation of the laser in the fundamental super mode of the coupled partial lasers formed by the individual pump currents is promoted, so that a spatially narrow remote field is generated.
The aforedescribed gain-guided diode lasers are single-beam laser light sources. Although, with the aforedescribed measures, an effect upon the intensity distribution of the remote field of the diode lasers is achieved, no lateral beam offset in a direction perpendicularly to the emission direction of the resonator can be achieved. However, this property is desirable in particular for the use of a multibeam laser light source for setting an image on an image carrier, in particular for the efficient setting of an image on a printing form in a printing form exposer or a direct imaging printing unit of a printing machine.
It is accordingly an object of the invention to provide a multibeam laser light source, particularly for a device for setting images on image carriers, which emits a plurality of light beams having projection points on a projection surface which exhibit a variable spacing from one another.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a multibeam laser light source, comprising a plurality of individual laser light sources arranged in an array and including a first and a second laser light source for emitting respective light beams spaced from one another, the first laser light source having a resonator with a given pump energy distribution therethrough, the spacing of the light beam emitted by the first laser light source from the light beam emitted by the second laser light source being variable by varying the given pump energy distribution through the resonator of the first laser light source.
In accordance with another feature of the invention, wherein the variation in the pump energy distribution is performable in at least one of two Cartesian spatial directions, at least approximately perpendicularly to an optical axis of the resonator.
In accordance with a further feature of the invention, the individual laser light sources are individually controllable.
In accordance with an added feature of the invention, the individual laser light sources are semiconductor lasers.
In accordance with an additional feature of the invention, the semiconductor lasers are gain-guided laser diodes.
In accordance with yet another feature of the invention, at least the first laser light source has a plurality of mutually insulated contacts for injecting current into the resonator.
In accordance with yet a further feature of the invention, the mutually insulated contacts are tracks extending at least approximately parallel to an optical axis of the resonator.
In accordance with yet an added feature of the invention, the mutually insulated contacts have an at least approximately uniform spacing from one another.
In accordance with yet an additional feature of the invention, the individual laser light sources are arranged on a substrate.
In accordance with still another feature of the invention, the individual laser light sources are located on a laser diode bar.
In accordance with still a further feature of the invention, the individual laser light sources are arranged in an array selected from the group thereof consisting of an at least approximately uniform and an at least approximately Cartesian array.
In accordance with still an added feature of the invention, the individual laser light sources are arranged at least approximately on a line.
In accordance with still an additional feature of the invention, the individual laser light sources are arranged at least on an approximately straight line.
In accordance with another feature of the invention, the multibeam laser light source further has a control unit assigned thereto, the control unit serving for controlling at least one of timed driving of the individual laser light sources and variation of pump energy distributions in the resonators of the respective individual laser light sources.
In accordance with a further feature of the invention, the multibeam laser light source further comprises a measuring device assigned to at least the first laser light source for distribution of the light emitted by the first laser light source, at least in one of two spatial directions perpendicular to an optical axis of the resonator.
In accordance with another aspect of the invention, there is provided an image-setting or imaging device for an image carrier, including a multibeam laser light source, comprising a plurality of individual laser light sources arranged in an array and including a first and a second laser light source for emitting respective light beams spaced from one another, the first laser light source having a resonator with a given pump energy distribution therethrough, the spacing of the light beam emitted by the first laser light source from the light beam emitted by the second laser light source being variable by varying the given pump energy distribution through the resonator of the first laser light source.
In accordance with a further feature of the invention, the image-setting device further comprises imaging optics having micro-optical components.
In accordance with an added aspect of the invention, there is provided a printing form exposer, including an image-setting or imaging device for an image carrier, having a multibeam laser light source, comprising a plurality of individual laser light sources arranged in an array and including a first and a second laser light source for emitting respective light beams spaced from one another, the first laser light source having a resonator with a given pump energy distribution therethrough, the spacing of the light beam emitted by the first laser light source from the light beam emitted by the second laser light source being variable by varying the given pump energy distribution through the resonator of the first laser light source.
In accordance with an additional aspect of the invention, there is provided a printing unit, including an image-setting or imaging device for an image carrier, having a multibeam laser light source, comprising a plurality of individual laser light sources arranged in an array and including a first and a second laser light source for emitting respective light beams spaced from one another, the first laser light source having a resonator with a given pump energy distribution therethrough, the spacing of the light beam emitted by the first laser light source from the light beam emitted by the second laser light source being variable by varying the given pump energy distribution through the resonator of the first laser light source.
In accordance with a concomitant feature of the invention, there is provided a printing press, provided with a printing unit, including an image-setting or imaging device for an image carrier, having a multibeam laser light source, comprising a plurality of individual laser light sources arranged in an array and including a first and a second laser light source for emitting respective light beams spaced from one another, the first laser light source having a resonator with a given pump energy distribution therethrough, the spacing of the light beam emitted by the first laser light source from the light beam emitted by the second laser light source being variable by varying the given pump energy distribution through the resonator of the first laser light source.
According to the invention, the multibeam laser light source with a plurality of individual laser light sources which are arranged in an array is distinguished by the fact that the spacing of the light beam emitted by a first laser light source of the plurality of laser light sources from a light beam emitted by a second laser light source of the plurality of laser light sources can be varied by varying the pump energy distribution through the resonator of the first laser light source. Herein, the arrangement in an array is to be understood to be that the laser light sources at least approximately all lie in a two-dimensional surface or on a one-dimensional curve. The spacing of the light beams from one another is to be understood in this connection as the spacing of the optical axis of the first laser light source from the optical axis of the second light source, measured at a comparable point, for example on the exit surfaces of the light or facets of the resonators of the laser light sources. The laser light sources are preferably arranged in the array in such a way that at least approximately parallel emission of the laser light beams in relation to one another occurs. Furthermore, it is preferable that varying the pump energy distribution can be performed for each of the plurality of individual laser light sources. The individual laser light sources can preferably be driven individually. Expressed in other words, the individual laser light sources of the multibeam laser light source can be single-beam laser light sources which are independent of one another.
In a preferred embodiment of the invention, the variation in the pump energy distribution is carried out in at least one of the two Cartesian spatial directions, at least approximately perpendicularly to the optical axis of the resonator. Furthermore, the pump energy distribution along the optical axis, at least on a section of the resonator, can be at least approximately independent of the distance from the exit mirror or from the exit surface of the light from the resonator.
It is particularly advantageously possible, in the multibeam laser light source according to the invention, to correct a pitch error, i.e., a deviation which, for example, is caused by production or manufacture, of the actual position of the optical axes of the individual laser light sources in the array, predefined or prescribed by the geometry of the laser, from a desired or required position, by carrying out a shift in the active region of one or more laser light sources at least approximately perpendicularly to the emission direction defined by the optical axis.
The individual laser light sources are preferably embodied as semiconductor lasers, in particular gain-guided laser diodes. At least the first laser light source of the plurality of laser light sources, preferably each of the individual laser light sources, has a plurality of mutually insulated contacts for injecting current into the resonator. The number of laser light sources is independent of the number of mutually insulated contacts. In particular, the mutually insulated contacts are tracks which extend at least approximately parallel to the optical axis of the resonator. A shift of the active region of one or more individual laser light sources at least approximately perpendicularly to the emission direction defined by the optical axis can then be achieved by varying the driving or controlling of the contacts. The mutually insulated contacts can have an at least approximately uniform spacing from one another.
In an advantageous development of the invention, the individual laser light sources of the multibeam laser light source are arranged on a substrate. Therefore, expressed in other words, the multibeam laser light source can be in particular a laser diode array or a laser diode bar. It can be used in continuous operation or in pulsed operation.
It is particularly advantageous if the individual laser light sources of the multibeam laser light source are arranged in an at least approximately uniform and/or at least approximately Cartesian array. Typically, the laser light sources can be arranged at least approximately on a line, in particular on a straight line. By such regular arrangements, use in an image-setting or imaging device is made considerably easier, because then the assignment of the image data of the individual image points to the image-setting channels formed by the light beams, by the so-called image-setting or imaging beams, satisfies simple rules. A variation in the spacing of a light beam emitted by a first light source from a light beam emitted by a second light source is consequently then only necessary to a slight extent, for example in order to correct production or manufacturing errors in the multibeam laser light source or construction errors, which in each case lead to deviations from a regular arrangement.
At this point, it should be noted generally that the feature of a variable spacing between the light beams emitted by a first and a second light source in the multibeam laser light source, a variable pitch spacing, can be used in at least two ways: Firstly, the variation in the pump energy distribution through the resonator can be performed for the calibration of the multibeam laser light source. The desired light beam spacing is set and the multibeam laser light source is then operated with the pump energy distribution required for this purpose. Secondly, it is also conceivable that an adjustable spacing is provided, i.e., the multibeam laser light source is operated in a first period, depending upon the purpose, with a first spacing between the light beams of a first and a second light source and, in a second period, is operated with a second spacing between the light beams of a first and a second light source. It is believed to be clear that both measures can also be taken in combination and result in advantageous possible uses due to the adjustable laser spacing.
In an advantageous embodiment, the multibeam laser light source has a control unit assigned thereto, which controls the timed driving of the laser light sources and/or the variation of the pump energy distributions in the resonators thereof.
The timed driving of the laser light sources can preferably also be carried out with a time delay in relation to one another. For this purpose, a delay device can be provided which, following the triggering of a first laser light source, effects the time-delayed triggering of all the other light sources of the plurality of light sources. The power supply to the multibeam laser light source can be provided by discrete electronics or by a microelectronic circuit which, optionally, can be integrated on the same holding element as the multibeam laser light source. Furthermore, provision can be made for a measuring device for the distribution of the light emitted by the first laser light source, at least in one of the two spatial directions at right angles to the optical axis, to be assigned at least to the first laser light source. Furthermore, automatic adjustment of the spacings between individual laser light sources to desired values, in particular by using the measured values from the measuring device for determining an actual value, can be provided. In an advantageous development of the invention, the output power of each laser light source can be stabilized by a closed control loop.
As already repeatedly mentioned hereinbefore, the multibeam light source according to the invention can advantageously be used in an image-setting or imaging device for an image carrier. Here, the image carrier can be in particular a printing form, a printing form precursor, which becomes a printing form as result of further process steps, or a film. In particular, it can be a printing form for offset printing. In a preferred embodiment, the image-setting or imaging device comprises imaging optics having micro-optical components. The individual components, in particular the micro-optical components, of the imaging optics can, in this regard, further be used to vary the propagation direction of the light or a light beam, for beam shaping or the like. In a further development of the invention, the light beams produced by the multibeam laser light source according to the invention are excited by a close-coupled microchip laser, the emitted radiation of which can be continuous or pulsed.
Due to the variable beam spacing of the light from the multibeam laser light source, it is advantageously possible to achieve variable spacing of the projection points of the laser light sources in the projection by reproducing or imaging optics onto a projection plane or projection surface. If the projection points are used to produce image points in an image-setting or imaging device according to the invention, there is implied a variable resolution, i.e., number of image points per unit length, of the image-setting or imaging device. In this case, in connection with the invention, it is unimportant whether adjacent image points are exposed simultaneously or, for example, are set at consecutive image-setting times within the context of a so-called interleaf process.
If, for setting an image on an image carrier which is moved relative to the image-setting device, which comprises a multibeam laser light source with light sources arranged in a one-dimensional array, delayed individual driving of the laser light sources is combined with a variation in the spacing of the light beams emitted by the individual laser light sources in the direction perpendicular to the relative movement between image-setting device and image carrier, it is possible to achieve a two-dimensional correction of the position of image points, by translation of the image point perpendicularly to the direction of the relative movement and by projection along the direction of the relative movement onto a one-dimensional curve.
An image-setting or imaging device according to the invention for an image carrier which is a printing form can be used with particular advantage in a printing form exposer or in a printing unit. A printing press according to the invention, which comprises a feeder, at least one printing unit and a delivery, is distinguished by the fact that the printing press has at least one printing unit with an image-setting or imaging device according to the invention. Here, the press can be a machine that processes sheet-like printing materials, which comprises at least one feeder, a printing unit and a delivery, or a web-processing machine, also additionally having a folder arranged downstream.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a multibeam laser light source with variable laser light-source spacing for setting images on printing forms, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.